1. Field of the Invention
The present invention relates to the preparation of a new composition of matter and its use in chemical and other fields. It particularly relates to a composition of matter useful for the detection of the presence of alkali metals, alkali metal hydroxides or alkali metal carbonates on surfaces.
2. Prior Art
Numerous chemical compositions and methods have been suggested heretofore for detecting leaks in vessels. U.S. Pat. No. 3,597,263 suggests a water leak detector, which may be provided in the form of a paint or adhesive tape for application to a metal surface. The indicators suggested comprise (a) a carrier and a strontium chromate/silver sulphate couple as the active indicator, or (b) a carrier and a potassium ferrocyanide/ferric sulphate-inert brightener couple as the active indicator, or (c) a carrier and a potassium ferrocyanide/cupric sulphate-inert brightener couple as the active indicator.
U.S. Pat. No. 3,287,156 suggests a leak-indicating coating for missiles and rockets. The suggested leak-indicating coating comprises an undercoating on the exterior side of the vessel and an overcoating on the undercoating. Each coating comprises a light-colored solid organic material selected from the group consisting of cellulose-base lacquers and solvent-type resins. The undercoating contains phenosafranine dispersed therein, and the overcoating contains a dispersion of phenolphthalein.
Other patents relating to the use of coatings for the detection of leaks are U.S. Pat. Nos. 1,478,445; 1,915,965; 2,228,737; 2,601,840; and 2,708,896.
U.S. Pat. No. 3,814,695 discloses a water washable penetrant composition for the detection of surface defects. The penetrant comprises a vehicle consisting of a vinyl-chloride, vinyl-acetate copolymer resin binder, a solvent and an alkylene oxide condensate non-ionic surfactant containing from about 1-2% by volume of a dye which is soluble in the vehicle.
U.S. Pat. No. 3,652,225 relates to a color method for detecting cracks in metal bodies. A color-forming aqueous acid indicating solution containing halide ions and a color-forming indicator is applied to the surface of a body to be tested. The solution is formulated so that it does not corrode to any significant extent the open surface portion of the body, but is sufficiently reactive to corrode the surface portion within cracks, resulting in the formation of metallic ions. The color-forming indicator is of the type which reacts with the thus-formed metal ions to form a distinctive colored compound at the crack location.
The foregoing methods and compositions, while useful in their respective fields, do not fulfill the need for a composition and method useful for the detection of alkali metals, alkali metal hydroxides or alkali metal carbonates on a metal surface. More particularly, it has been found that a residue of an alkali metal such as sodium on a metal surface will react with water and carbon dioxide in the air to form sodium hydroxide and carbonate, respectively. Even small amounts of any one of these materials on the surface of a metal part for an extended period of time can cause localized surface corrosion, which could result in a failure of the part when it is placed in service. In a nuclear reactor which utilizes a liquid alkali metal such as sodium, potassium or mixtures thereof as a heat exchange fluid, a significant number of parts are exposed to the alkali metal and frequently may have to be removed for cleaning, maintenance or the like. Obviously, there is a need for a method of ensuring that all of the alkali metal has been removed from the surfaces of the part prior to its being exposed to the atmosphere for any extended period of time or being returned to service in the liquid metal environment.